Microstructured fiber interface coatings for composites

ABSTRACT

Disclosed is a coated ceramic fiber including a silicon carbide coating layer adjacent to the ceramic fiber and a silicon dioxide coating layer adjacent to the silicon carbide coating layer, wherein the silicon dioxide coating layer forms micro cracks after a crystal structure transformation. The coated ceramic fiber may be included in a composite material having a ceramic matrix.

BACKGROUND

Exemplary embodiments pertain to the art of composites, includingceramic matrix composites.

Composite components are finding increased use into aerospaceapplications due to their unique, tailorable properties which can resultin significant weight savings, increased performance and durability, aswell as reductions in specific fuel consumption. In particular, gasturbine engines, such as aircraft engines, operate in severeenvironments and show significant benefit from incorporation ofcomposite materials. Additionally, other aerospace components, such asbrakes, can benefit from incorporating composite materials.

As an example, ceramic matrix composite (CMC) components have desirablehigh temperature mechanical, physical, and chemical properties whichallow gas turbine engines to operate at much higher temperatures withsignificant weight savings as compared to current engines withsuperalloy components. As opposed to traditional, monolithic ceramics,CMCs exhibit a significant amount of damage tolerance when under anapplied load. This damage tolerance is due in part to the formation ofmultiple matrix cracks that aid in the redistribution of stresses to thehigh strength fibers.

The formation of matrix cracks can extend to the fiber and damage to thefiber may negatively impact the strength of the composite. Interfacecoatings have been used to address this issue. As CMCs, along with manyother composites, are used under harsh environmental conditions improvedinterface coatings are desired.

BRIEF DESCRIPTION

Disclosed is a coated ceramic fiber including a silicon carbide coatinglayer adjacent to the ceramic fiber and a silicon dioxide coating layeradjacent to the silicon carbide coating layer, wherein the silicondioxide coating layer forms micro cracks after a crystal structuretransformation.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the silicon dioxidecoating layer has a thickness of 50 nanometers (nm) to 10,000 nm, or,100 to 1,000 nm. Additionally, in some embodiments, the silicon carbidecoating layer has a thickness of 1000 nm to 20,000 nm, or, 2,000 to10,000 nm.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the silicon dioxidecoating layer is in β cristobalite form which forms micro cracks aftertransforming to α cristobalite form.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the coated ceramicfiber further includes an additional coating layer adjacent to thesilicon dioxide coating layer. The additional coating layer compositioncan be the same as the silicon carbide coating layer or different fromthe silicon carbide coating layer.

Also disclosed is a composite material including a ceramic matrixmaterial and a plurality of coated ceramic fibers embedded within thematrix material. The coating on the fibers is a multi-layer interfacecoating. The multi-layer interface coating includes a silicon carbidecoating layer adjacent to the plurality of fibers, and a silicon dioxidecoating layer adjacent to the silicon carbide coating layer, wherein thesilicon dioxide coating layer has micro cracks resulting from a crystalstructure transformation.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the silicon dioxidecoating layer has a thickness of 50 nanometers (nm) to 10,000 nm, or,100 to 1,000 nm. Additionally, in some embodiments, the silicon carbidecoating layer has a thickness of 1000 nm to 20,000 nm, or, 2,000 to10,000 nm.

In addition to one or more of the features described above, or as analternative to any of the foregoing embodiments, the multi-layerinterface coating includes an additional coating layer adjacent to thesilicon dioxide coating layer. The additional coating layer can besilicon carbide coating layer.

Also disclosed is a method for forming a multi-layer interface coatingonto a ceramic fiber including depositing a silicon carbide coatinglayer onto the fiber, oxidizing a portion of the silicon carbide coatinglayer to form a silicon dioxide coating layer, and crystallizing thesilicon dioxide to beta cristobalite. The method may further includedepositing an additional layer on the silicon dioxide coating layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

The FIGURE shows a representative interface coating and method ofmaking.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the FIGURE.

Composites exhibit a significant amount of damage tolerance when underan applied load. In ceramic matrix composites (CMC) in particular, thisdamage tolerance is due to the formation of multiple matrix cracks thataid in the redistribution of stresses. However, the formation of matrixcracks can result in environmental exposure to the fiber and fiberinterface coating. The fiber interface coating protects the fiber fromthe environmental exposure and provides a weak interface to allow forcomposite behavior.

The multi-layer interface coating described herein provides a weakinterface with the fiber to allow for composite behavior and alsoprovides environmental protection. The multiple layers can prevent crackpropagation from reaching the fibers and protect the fiber fromenvironmental degradation. In particular, the silicon dioxide layer is acrystalline material which goes through a crystal structuretransformation after a heat treatment or under conditions of normal use.The crystal structure transformation results in the presence of microcracks which can deflect any matrix cracks from reaching the fiber.

Referring now to the FIGURE a coated ceramic fiber for use in acomposite is shown. The coated ceramic fiber includes ceramic fiber 12and a multi-layer interface coating 22. The multi-layer interfacecoating 22 as shown includes three coating layers 24, 32 and 28. Itshould be appreciated that the additional coating layer 28 is optional.Exemplary ceramic fiber materials include silicon carbide, carbon,aluminum oxide, mullite, hafnium carbide, zirconium carbide, tantalumcarbide, niobium carbide, boron carbide, titanium carbide, hafniumboride, zirconium boride, tantalum boride, niobium boride, titaniumboride, and combinations thereof. Silicon carbide fibers have residualcarbon which distinguishes the fibers compositionally from the siliconcarbide coating layer which does not have carbon.

The first interface layer 24 includes silicon carbide. A portion of thesilicon carbide layer is oxidized to form amorphous silicon dioxide. Theadditional coating layer 28, may include silicon carbide, zirconium,zirconium boride or a combination thereof.

The silicon carbide layer may have a thickness of 1000 nm to 20,000 nm,or, 2,000 nm to 10,000 nm. The silicon dioxide layer may have athickness of 50 nm to 10,000 nm, or, 100 nm to 1,000 nm. The additionalcoating layer may have a thickness of 1000 nm to 20,000 nm, or, 2000 nmto 10,000 nm.

The silicon carbide layer is deposited on the ceramic fiber by chemicalvapor deposition (shown as step 110). The combination of the siliconcarbide layer and the ceramic fiber are then heat treated in thepresence of oxygen to oxidize a portion of the silicon carbide layer toform a silicon dioxide 30 (shown as step 120) which is initiallyamorphous.

An additional coating layer or at least portion of the matrix is thendeposited on the silicon dioxide layer (shown as step 130) by, forexample, chemical vapor deposition, after which the fiber with themultilayer coating is subjected to a heat treatment (shown as step 140)to crystallize the silicon dioxide. Exemplary additional coating layermaterials include zirconium, silicon carbide, zirconium boride orcombinations thereof. Exemplary matrix materials include siliconcarbide, aluminum oxide, mullite, cordierite, and combinations thereof.

The heat treatment crystallizes the silicon dioxide 30 and formsbeta-cristobalite 26 and upon cooling (shown as step 150)alpha-cristobalite 32 forms with a volume reduction which results inmicro cracking. Exemplary heat treatment temperatures (step 140) 1200 to1650° C., or, 1300 to 1600° C. Exemplary times for the heat treatmentinclude 1 minute to 100 hours, or, 1 minutes to 50 hours.

The micro cracks in the silicon dioxide coating layer provide protectionto the fiber from matrix cracking by deflecting the cracks into thesilicon dioxide layer. The first interlayer provides environmentalprotection to the fiber so the combination of layers results in acomposite with more robust properties. The third layer, when present,protects the micro cracked second layer.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. The term “adjacent to” is defined as being incontact with the underlying material. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, element components, and/or groups thereof.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A coated ceramic fiber comprising a siliconcarbide coating layer adjacent to the ceramic fiber, and a silicondioxide coating layer adjacent to the silicon carbide coating layer,wherein the silicon dioxide coating layer forms micro cracks after acrystal structure transformation.
 2. The coated ceramic fiber of claim1, wherein the silicon dioxide coating layer has a thickness of 50 nm to10,000 nm.
 3. The coated ceramic fiber of claim 1, wherein the siliconcarbide coating layer has a thickness of 1000 nm to 20,000 nm.
 4. Thecoated ceramic fiber of claim 1, wherein the silicon dioxide coatinglayer includes silicon dioxide in β cristobalite form which forms microcracks after transforming to α cristobalite form.
 5. The coated ceramicfiber of claim 1, further comprising an additional coating layeradjacent to the silicon dioxide coating layer.
 6. The coated ceramicfiber of claim 5, wherein the additional coating layer has the samecomposition as the silicon carbide coating layer.
 7. The coated ceramicfiber of claim 5, wherein the additional coating layer has a differentcomposition from the silicon carbide coating layer.
 8. A compositematerial comprising a ceramic matrix material and a plurality of ceramicfibers embedded within the ceramic matrix material wherein the pluralityof ceramic fibers comprise a multi-layer interface coating and themulti-layer interface coating comprises a silicon carbide coating layeradjacent to the plurality of ceramic fibers, and a silicon dioxidecoating layer deposited onto the silicon carbide coating layer, whereinthe silicon dioxide coating layer forms micro cracks after a crystalstructure transformation.
 9. The composite material of claim 8, whereinthe silicon dioxide coating layer has a thickness of 50 nm to 10,000 nm.10. The composite material of claim 8, wherein the silicon carbidecoating layer has a thickness of 1000 nm to 20,000 nm.
 11. The compositematerial of claim 8, wherein the silicon dioxide coating layer includessilicon dioxide in α cristobalite form.
 12. The composite material ofclaim 8, wherein the multi-layer interface coating further comprises anadditional interface coating layer adjacent to the silicon dioxidecoating layer.
 13. The coated ceramic fiber of claim 12, wherein theadditional interface coating layer has the same composition as thesilicon carbide coating layer.
 14. The coated ceramic fiber of claim 12,wherein the additional interface coating layer has a differentcomposition from the silicon carbide coating layer.
 15. A method forforming a multi-layer interface coating onto a ceramic fiber comprisingdepositing a silicon carbide coating layer onto the fiber, oxidizing aportion of the silicon carbide coating layer to form a silicon dioxidecoating layer, and crystallizing the silicon dioxide layer to betacristobalite.
 16. The method of claim 15, further comprising depositingan additional coating layer on the silicon dioxide coating layer priorto crystallizing the silicon dioxide.